A need has developed in industry for an end effector that can be picked up and manipulated by a robot and used to grasp a workpiece and position that workpiece at a precisely predetermined position against a panel, and then drill a pair of coordination holes through the workpiece and the panel that can be used for precisely locating the workpiece on the panel. An end effector with this capability would be useful in many traditional manufacturing applications, but finds especially significant value in a new manufacturing technique known as "virtual tooling assembly," which is disclosed and claimed in a concurrently filed patent application Ser. No. 07/964,533 entitled "PANEL AND FUSELAGE ASSEMBLY."
In traditional manufacturing, parts are normally held in tooling fixtures and assembly jigs to accurately locate the parts by butting their edges against hard stops on the tooling. From those stops, locations on the part are determined for holes, fasteners, and other manufacturing processes which are performed on the part. Assuming that the part is located properly on the tooling and that the drill guides and other parts of the tooling for performing the manufacturing processes have been accurately located, the part will be accurately manufactured. However, in the real-life environment of a factory, the tooling receives some heavy and sometimes abusive use and the accuracy of the stops, drill guides, and other elements of the tooling frequently become worn, damaged, or otherwise out of adjustment. When this happens, the manufacturing processes on the part can be performed at an incorrect location on the part resulting in slight misalignment of the elements of the finely manufactured product, or if the misalignment is severe, a completely rejected part. The result is a degradation of quality and increased cost of manufacturing.
A new manufacturing technique has been invented called "soft tooling" or "virtual tooling" which eliminates the need for hard tooling used for the positioning of holes, fasteners, and other manufacturing processes. The virtual tooling technique uses digital information from the original engineering definition of the part to locate the holes and other items on the part without reference to hard tooling reference stops. One technique is to mount the part, such as a panel, on a fixture which holds it in a fixed position and contour but without reliance on the position of any hard stops on the fixture. The panel is then routed around its entire edge to give it the precise exterior dimensions required by the original engineering data. The holes, fasteners, and parts which are to be placed at particular positions on the panel, are located by coordination holes, also known as "positioning holes," drilled in the panel by a drilling end effector held by a highly accurate robot. The positioning of the robot is accomplished by software using positioning information derived from the engineering data for that part, so the part as manufactured is always in conformance with the most current engineering drawing of that part and does not rely on the accuracy of any hard tooling.
Any other components which must be attached to the panel are drilled at the same time or on another fixture so that the positioning holes in the panel and on the other components are precisely accurate, well within the required tolerance. After the positioning holes have been drilled, the panel and other components are removed from the fixture, and the components may be repositioned and temporarily fastened to the panel using the positioning holes. They are then drilled and permanently fastened to the panel with rivets or other permanent fasteners. Alternatively, the part may be temporarily fastened to the panel immediately after drilling the coordination holes by inserting temporary fasteners through the positioning holes while the part is still being held by the positioning and drilling end effector to secure the part on the panel at the correct location, thereby obviating the additional manufacturing step of matching the part with the correct location during permanent assembly of the part on the panel. Both of these techniques accurately locate the parts on the panel, so the care and recalibration of hard tooling becomes an obsolete requirement.
In order to eliminate the need for hard tooling positioning stops for accurately locating the components relative to the part in which the coordination positioning holes are being drilled, it would be useful for the end effector carried by the robot to be capable of positioning those components exactly in the desired position to ensure that the hole in the component and the hole in the part are drilled in the right position. One such end effector is disclosed in U.S. Pat. No. 5,127,139 entitled "STRINGER CLIP END EFFECTOR" by McCowin, et al. Another end effector required for aircraft manufacturing is one which aligns a channel-shaped workpiece such as a stringer at a desired position with respect to the drill axis and holds the stringer in that position while it drills a hole in the channel at the desired lateral position and at the desired position along its length. This end effector is disclosed in U.S. patent application Ser. No. 07/996,806 entitled WORKPIECE POSITIONING AND DRILLING END EFFECTOR filed on Dec. 29, 1992 by Peter McCowin, now U.S. Pat. No. 5,299,894.
A fixture which could be used to hold the panel while the parts are being positioned and drilled is disclosed in U.S. Pat. No. 5,249,785 entitled "Reconfigurable Fixture" filed on Apr. 20, 1992 by Paul Nelson. This fixture includes an array of headers having suction-operated holders for securely holding the panel in the desired position. The panel is unsupported between the headers and is fairly thin, so it could be dimpled or wrinkled by pressing the part with excessive force against the panel. However, the part should be pressed against the panel with sufficient force to prevent the formation of burrs on the part or the panel during the drilling of the coordination holes.
Because the "virtual tooling" manufacturing system relies on the accuracy of the robot and the end effector, it is desirable to incorporate a measuring system to confirm that the robot and the end effector are being positioned and configured accurately. In this way, errors in positioning of parts and drilling of coordination holes would go undetected by the operator only if both the machines and the measuring system were to independently and simultaneously go out of adjustment by exactly the same amount and in the same direction.
The coordination holes in the part may be at different places on different parts, so it would be desirable to be able to reconfigure the end effector to be able to position the pair of coordination holes at desired edge spacing from the flange of the part, and at desired separation between the two coordination holes. The adjustment to achieve these variable positioning of the coordination holes in the parts should be done remotely and automatically without requiring time consuming and error prone manual adjustment by the operator or down time of the manufacturing cell while the adjustment is being made.